Chatzos-based changes to ZmanimCalendar

1. Add setting useAstronomicalChatzos (defaulted to true) to keep the mistaken compat break introduced in the v2.5.0 release.
2. Add setting useAstronomicalChatzosForOtherZmanim (defaulted to false).
3. Add getChatzosAsHalfDay() to retain the old behavior of chatzos being halfway between sunrise and sunset.
4. Use useAstronomicalChatzos to control if getChatzos() returns getSunTransit() (astronomical chatzos) or getChatzosAsHalfDay().
5. Add getHalfDayBasedZman(Date startOfHalfDay, Date endOfHalfDay, double hours) to allow other zmanim to be impacted by chatzos.
6. Use useAstronomicalChatzosForOtherZmanim in getMinchaGedola as an experiment showing the use of the setting.
7. Small JavaDoc tweaks